Sputtering is known in the art as a technique for depositing layers or coatings onto substrates such as glass substrates. For example, a low-emissivity (low-E) coating can be deposited onto a glass substrate by successively sputter-depositing a plurality of different layers onto the substrate. As an example, a low-E coating may include the following layers in this order: glass substrate/SnO2/ZnO/Ag/ZnO, where the Ag layer is an IR reflecting layer and the metal oxide layers are dielectric layers. In this example, one or more tin (Sn) targets may be used to sputter-deposit the base layer of SnO2, one or more zinc (Zn) inclusive targets may be used to sputter-deposit the next layer of ZnO, an Ag target may be used to sputter-deposit the Ag layer, and so forth. The sputtering of each target is performed in a chamber housing a gaseous atmosphere (e.g., a mixture of Ar and O gases in the Sn and/or Zn target atmosphere(s)). Example references discussing sputtering and devices used therefore include U.S. Pat. Nos. 8,192,598, 6,736,948, 5,427,665, 5,725,746 and 2004/0163943, the entire disclosures of which are all hereby incorporated herein by reference.
A sputtering target (e.g., cylindrical rotatable magnetron sputtering target) typically includes a cathode tube within which is a magnet array. The cathode tube is often made of stainless steel. The target material is typically formed on the tube by spraying, casting or pressing it onto the outer surface of the stainless steel cathode tube. Often, a bonding or backing layer is provided between the tube and the target to improve bonding of the target material to the tube. Each sputtering chamber includes one or more targets, and thus includes one or more of these cathode tubes. The cathode tube(s) may be held at a negative potential (e.g., −200 to −1500 V), and may be sputtered when rotating. When a target is rotating, ions from the sputtering gas discharge are accelerated into the target and dislodge, or sputter off, atoms of the target material. These atoms, in turn, together with the gas form the appropriate compound (e.g., tin oxide) that is directed to the substrate in order to form a thin film or layer of the same on the substrate.
In addition to the quality of the coating the magnetron deposits upon the substrate, dependability and serviceability of the magnetron is an issue. This is not an easy task taking into account the constraints of the process that is involved. A cylindrical magnetron sputters material from a rotating target tube onto the substrate as it is transported past the target. In order to coat such a large piece of glass or the like the target tube can be up to 15 feet in length and up to 6 inches or more in diameter and can weigh up to 1700 pounds for example. Another complication is that the sputtering actually erodes the target tube during the sputtering process, so the target tube is constantly changing shape during its serviceable lifetime. And the sputtering process can require that an extremely high AC or DC power (e.g., 800 Amps DC, 150 kW AC) be supplied to the target in certain instances. This power transfer creates significant heat in the target tube and the surrounding components, which must be cooled in order to assure proper performance and to avoid failure of the magnetron. Thus, it is known to pump water through the center of the rotating target tube at high pressure and flow rate to cool the target.
FIG. 1 is a side plan view of a rotating sputtering target and conventional endblock. FIG. 1 illustrates that the rotating target 1 is supported on one end by an endblock 3. The endblock 3 may be supported by and/or attached to a wall or ceiling 5 of a sputtering chamber 8 in a sputtering apparatus 7. Outside of the sputtering chamber(s) 8, the sputtering apparatus is at atmospheric pressure 9. In FIG. 1, reference numeral 9 indicates areas at atmospheric pressure. Efficient and effective sputtering requires that the sputtering process take place in a vacuum or a reduced pressure relative to atmosphere—in FIG. 1 the chamber 8 (other than the endblock 3) is under vacuum and thus is at pressure less than atmospheric pressure. The rotating target system is designed to have a robust sealing system, including seals 11 and 12 to prevent pressure or vacuum leaks between the low pressure areas 8 and the atmospheric pressure areas 9.
Electrically conductive brushes 15 provide for electrical contact and thus a power connection between the collector and the rotor. In the conventional system of FIG. 1, the brushes 15 that provide the electrical power connection between the collector and rotor are located in an area 9 at atmospheric pressure.
It has surprisingly been found that a new design that includes locating the electrical contact(s) (e.g., brushes) between the collector and rotor in an area under vacuum (as opposed to in an area at atmospheric pressure as in conventional FIG. 1) provides for significant advantages over the conventional design. Moving the power connection between the rotor and collector to an area under vacuum (an area at a pressure less than atmospheric pressure), for example, allows for a structure where both the rotor and collector can be efficiently cooled (e.g., water cooled) which has surprisingly been found to allow the sputtering rate to be improved (e.g., up to a 20% improvement in sputtering rate has surprisingly been found compared to the conventional FIG. 1 design). A rotating sputtering target, such as a magnetron sputtering target, is often supported by two endblocks—one at each end of the target. One or both of the endblocks for supporting a rotating target may be designed in accordance with example embodiments of this invention.
In example embodiments of this invention, there is provided a sputtering apparatus comprising: at least one endblock for supporting an end of a cylindrical rotatable sputtering target, the endblock including a fixed conductive collector, and a rotatable conductive rotor for rotating with the cylindrical sputtering target during sputtering operations; the endblock further including an electrical power transfer structure (e.g., conductive brush(es)) located between the fixed conductive collector and the rotatable rotor for allowing electrical power to be transferred from the collector to the rotor; a first cooling area through which liquid flows for cooling the fixed conductive collector, the first cooling area being located around at least a portion of the fixed conductive collector and being substantially concentric with the fixed conductive collector; a second cooling area, separate from the first cooling area, through which liquid flows for cooling the rotor and target, the second cooling area being at least partially surrounded by the rotor, and wherein the liquid in the second cooling area flows in at least a direction that is substantially parallel to an axis about which the target and rotor are to rotate; wherein the liquid in the first cooling area flows around the axis about which the target and rotor are to rotate; and wherein the electrical power transfer structure, the rotor, and the collector are each located (partially or fully) in an area under vacuum having pressure less than atmospheric pressure (e.g., so that there is no significant difference in pressure therebetween).
Unless otherwise stated or indicated, “fixed” as used herein when referring to an element being “fixed” means that the element at issue does not rotate together with the rotor or target tube during sputtering operations.